The present invention relates to fuel control systems, and more particularly, to a method of determining the fuel composition in a flexible fueled vehicle.
Environmental and energy independence concerns have stimulated the development of alternative transportation fuels for use in automobiles and other vehicles. In addition to gasoline as the traditional fuel used in spark-ignition engines, hydrogen, natural gas, alcohol fuel or fuel mixtures of gasoline and alcohol fuel, for example, are used as fuels in spark-ignition or internal combustion engines and are hereafter referred to as spark-ignition fuels. Alcohol fuels are popular alternative fuels and include methanol, ethanol, butanol, and others fuels known in the art.
Different spark-ignition fuels have varying physical properties. As a result, internal combustion engines operate differently when supplied with different fuels. Prior art attempts to operate an engine with multiple spark-ignition fuels modified the engine to run with a “worst case” fuel composition. However, the use of such a variety of spark-ignition fuels produces many scenarios wherein a “worst case” tuned engine does not operate with an acceptably high efficiency. Modern engines, equipped with variable ignition and valve actuation, offer the possibility of changing many engine settings to optimize engine behavior for each fuel used. Therefore, it is desired to determine the composition of the spark-ignition fuel being supplied to the engine and modify the engine's operation settings accordingly such that the engine may operate with the best possible efficiency.
There have been several prior art attempts to accurately and effectively determine and/or monitor the fuel composition of an internal combustion engine. The most straightforward solution is to implement a fuel composition sensor. However, fuel composition sensors can be prohibitively expensive or provide limited reliability. Other solutions include monitoring the exhaust system using existing exhaust sensors and control systems.
U.S. Pat. Nos. 4,920,494 and 4,905,649 both provide systems that utilize combustion chamber pressure data taken during a combustion event to determine a fuel composition and make corrections to the engine's operation settings.